Most pacemaker designs utilize a metallic housing to isolate a pacemaker's contents from the implanted environment in which it is installed. The material selected must be inert to the patient and must protect the electronic circuitry from bodily fluids. Titanium is a typical housing material. Electrical leads for pacemaker signals must be connected to the pacemaker using electrical feed-throughs that preserve the environmental integrity of the housing. Since the housing is made of metal and tends to exhibit the properties of a Faraday cage, RF communications designs between a pacemaker and radios outside the patient's body have traditionally used low frequency, near field solutions that can traverse the housing. Also, since a pacemaker is battery powered, available transmitter power is limited. As such, near field solutions dramatically limit range, and since these solutions are also low frequency, data rates are limited. Any RF communications systems design utilizing implantable medical devices must consider average and peak power consumption, FCC constraints (or other regulatory constraints, such as frequency of operation, bandwidth, and radiated power), antenna performance, data rate, exposure of pacemaker circuitry to RF radiation (particularly low level ECG signals), size of antenna system and associated RF circuitry, reliability, and cost (both component and manufacturing).
To maximize range and data rate, it is desirable to use a high frequency solution. The challenge is to develop a high frequency design that has acceptable antenna performance, while minimizing size, power consumption, and radiation of pacemaker circuitry. Some existing high frequency designs use an external antenna which is attached to the outside of the pacemaker housing using some type of electrical feed-throughs to connect the RF circuitry inside the pacemaker housing to the external antenna.
The present invention leverages upon several different technologies to create an antenna design and RF system that is more optimal for implanted applications.